Active triangulation technology may rely upon matching, using an epipolar constraint, detected projected pattern features to features in the original pattern that was projected onto an imaged scene. A straightforward way to do that is to detect a pattern feature in an image of a reflected portion of a projected structured light pattern, use a stereo set of calibration parameters, estimate the corresponding Epipolar line through the projector plane, find a corresponding feature on (or closest to) the line (in the projected structured light pattern), and triangulate to find 3D coordinates of the feature again, using the calibration parameters.
This strategy works well as long as the system's calibration is intact. Environmental changes as well as mechanical shocks and strains influence both intrinsic and extrinsic calibration parameters. As a result, estimated Epipolar lines are incorrect, which leads in turn to faulty feature matching. Epipolar mismatches have much stronger impact on a resulting point cloud than triangulation errors. The latter produce a distorted point cloud, with degree of distortion depending smoothly on the calibration errors. The former, however, can result in complete and abrupt disintegration of the point cloud.